There's a Cow Under my Bed! By Valerie Sherrard, illustrated by David Jardine

From chapters.ca:
Poor Oscar! His life is plagued with creatures he can't see. A cow licks his head every night, and that's just for starters. He's also had ants in his pants and a frog in his through, but try as he might, he can't seem to find them. Even so, he knows they're there. How? Because his mother tells him so!